logfactoryimpl.java

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    /**
     * Set the configuration attribute with the specified name.  Calling
     * this with a <code>null</code> value is equivalent to calling
     * <code>removeAttribute(name)</code>.
     *
     * @param name Name of the attribute to set
     * @param value Value of the attribute to set, or <code>null</code>
     *  to remove any setting for this attribute
     */
    public void setAttribute(String name, Object value) {

        if (value == null) {
            attributes.remove(name);
        } else {
            attributes.put(name, value);
        }

    }


    // ------------------------------------------------------ Protected Methods



    /**
     * Return the fully qualified Java classname of the {@link Log}
     * implementation we will be using.
     */
    protected String getLogClassName() {

        // Return the previously identified class name (if any)
        if (logClassName != null) {
            return logClassName;
        }

        logClassName = (String) getAttribute(LOG_PROPERTY);

        if (logClassName == null) { // @deprecated
            logClassName = (String) getAttribute(LOG_PROPERTY_OLD);
        }

        if (logClassName == null) {
            try {
                logClassName = System.getProperty(LOG_PROPERTY);
            } catch (SecurityException e) {
                ;
            }
        }

        if (logClassName == null) { // @deprecated
            try {
                logClassName = System.getProperty(LOG_PROPERTY_OLD);
            } catch (SecurityException e) {
                ;
            }
        }

        if ((logClassName == null) && isLog4JAvailable()) {
            logClassName = "org.apache.commons.logging.impl.Log4JLogger";
        }

        if ((logClassName == null) && isJdk14Available()) {
            logClassName = "org.apache.commons.logging.impl.Jdk14Logger";
        }

        if ((logClassName == null) && isJdk13LumberjackAvailable()) {
            logClassName = "org.apache.commons.logging.impl.Jdk13LumberjackLogger";
        }

        if (logClassName == null) {
            logClassName = "org.apache.commons.logging.impl.SimpleLog";
        }

        return (logClassName);

    }


    /**
     * <p>Return the <code>Constructor</code> that can be called to instantiate
     * new {@link org.apache.commons.logging.Log} instances.</p>
     *
     * <p><strong>IMPLEMENTATION NOTE</strong> - Race conditions caused by
     * calling this method from more than one thread are ignored, because
     * the same <code>Constructor</code> instance will ultimately be derived
     * in all circumstances.</p>
     *
     * @exception LogConfigurationException if a suitable constructor
     *  cannot be returned
     */
    protected Constructor getLogConstructor()
        throws LogConfigurationException {

        // Return the previously identified Constructor (if any)
        if (logConstructor != null) {
            return logConstructor;
        }

        String logClassName = getLogClassName();

        // Attempt to load the Log implementation class
        Class logClass = null;
        Class logInterface = null;
        try {
            logInterface = loadClass(LOG_INTERFACE);
            logClass = loadClass(logClassName);
            if (logClass == null) {
                throw new LogConfigurationException
                    ("No suitable Log implementation for " + logClassName);
            }
            if (!logInterface.isAssignableFrom(logClass)) {
                Class interfaces[] = logClass.getInterfaces();
                for (int i = 0; i < interfaces.length; i++) {
                    if (LOG_INTERFACE.equals(interfaces[i].getName())) {
                        throw new LogConfigurationException
                            ("Invalid class loader hierarchy.  " +
                             "You have more than one version of '" +
                             LOG_INTERFACE + "' visible, which is " +
                             "not allowed.");
                    }
                }
                throw new LogConfigurationException
                    ("Class " + logClassName + " does not implement '" +
                     LOG_INTERFACE + "'.");
            }
        } catch (Throwable t) {
            throw new LogConfigurationException(t);
        }

        // Identify the <code>setLogFactory</code> method (if there is one)
        try {
            logMethod = logClass.getMethod("setLogFactory",
                                           logMethodSignature);
        } catch (Throwable t) {
            logMethod = null;
        }

        // Identify the corresponding constructor to be used
        try {
            logConstructor = logClass.getConstructor(logConstructorSignature);
            return (logConstructor);
        } catch (Throwable t) {
            throw new LogConfigurationException
                ("No suitable Log constructor " +
                 logConstructorSignature+ " for " + logClassName, t);
        }
    }


    /**
     * MUST KEEP THIS METHOD PRIVATE.
     *
     * <p>Exposing this method outside of
     * <code>org.apache.commons.logging.LogFactoryImpl</code>
     * will create a security violation:
     * This method uses <code>AccessController.doPrivileged()</code>.
     * </p>
     *
     * Load a class, try first the thread class loader, and
     * if it fails use the loader that loaded this class.
     */
    private static Class loadClass( final String name )
        throws ClassNotFoundException
    {
        ClassLoader threadCL = getContextClassLoader();
        if (threadCL != null) {
            try {
                return threadCL.loadClass(name);
            } catch( ClassNotFoundException ex ) {
                // ignore
            }
        }
        return Class.forName( name );
    }


    /**
     * Is <em>JDK 1.3 with Lumberjack</em> logging available?
     */
    protected boolean isJdk13LumberjackAvailable() {

        try {
            loadClass("java.util.logging.Logger");
            loadClass("org.apache.commons.logging.impl.Jdk13LumberjackLogger");
            return (true);
        } catch (Throwable t) {
            return (false);
        }

    }


    /**
     * <p>Return <code>true</code> if <em>JDK 1.4 or later</em> logging
     * is available.  Also checks that the <code>Throwable</code> class
     * supports <code>getStackTrace()</code>, which is required by
     * Jdk14Logger.</p>
     */
    protected boolean isJdk14Available() {

        try {
            loadClass("java.util.logging.Logger");
            loadClass("org.apache.commons.logging.impl.Jdk14Logger");
            Class throwable = loadClass("java.lang.Throwable");
            if (throwable.getDeclaredMethod("getStackTrace", null) == null) {
                return (false);
            }
            return (true);
        } catch (Throwable t) {
            return (false);
        }
    }


    /**
     * Is a <em>Log4J</em> implementation available?
     */
    protected boolean isLog4JAvailable() {
        try {
            loadClass("org.apache.log4j.Logger");
            loadClass("org.apache.commons.logging.impl.Log4JLogger");
            return (true);
        } catch (Throwable t) {
            return (false);
        }
    }


    /**
     * Create and return a new {@link org.apache.commons.logging.Log}
     * instance for the specified name.
     *
     * @param name Name of the new logger
     *
     * @exception LogConfigurationException if a new instance cannot
     *  be created
     */
    protected Log newInstance(String name) throws LogConfigurationException {

        Log instance = null;
        try {
            Object params[] = new Object[1];
            params[0] = name;
            instance = (Log) getLogConstructor().newInstance(params);
            if (logMethod != null) {
                params[0] = this;
                logMethod.invoke(instance, params);
            }
            return (instance);
        } catch (InvocationTargetException e) {
            Throwable c = e.getTargetException();
            if (c != null) {
                throw new LogConfigurationException(c);
            } else {
                throw new LogConfigurationException(e);
            }
        } catch (Throwable t) {
            throw new LogConfigurationException(t);
        }

    }


}